The present invention relates to machines for converting straight or coiled wire into undulate wire, especially into a meandering wire which is ready to be converted into so-called Wire-O (trademark) binders for use in steno pads, note books, calendars, exercise books and analogous stationery products. More particularly, the invention relates to improvements in wire forming machines wherein a length of running straight or coiled wire can be converted into undulate wire of the type having hairpin-shaped sections or prongs alternating with straight sections or webs which connect the open ends of neighboring hairpin-shaped sections to each other and can be said to constitute the back of a substantially comb-like product.
Undulate products of the aforediscussed type are converted into binders by imparting to them a C-shaped or trough-shaped outline and by subdividing them into binder blanks of desired length. Such blanks are thereupon introduced into the perforations of stacks of superimposed sheets to hold the sheets together as soon as the blanks are closed by causing the tips of the prongs to come close to or to actually contact the webs i.e., by converting the substantially C-shaped blanks into substantially tubular binders. The perforations form a row along one edge of each stack and enable the sheets to pivot about the axis which is defined by the respective binder.
In accordance with a heretofore known proposal, a length of wire is converted into an undulate product by alternately looping the wire about successive pins or dogs of two rows of pins or dogs (hereinafter called pins) and by thereupon changing the distance between the two rows so that the wire is stretched and undergoes permanent deformation as a result of elongation beyond the elastic limit of its material, i.e., the pattern which is imparted by the two rows of pins is "frozen" into the resulting undulate product. The wire hugs the two rows of pins upon completion of the stretching operation to thus exhibit a number of prongs which alternate with the aforementioned webs. The pins of one row are configurated to form the webs, and the pins of the other row are configurated to form the tips of the prongs. Reference may be had to U.S. Pat. Nos. 3,691,808, 3,805,579, 4,047,544 and 4,165,767. A drawback of such apparatus is that the wire is likely to break when the operating speed is increased beyond a relatively low limit, namely, below a limit which must be exceeded if the machine is to satisfy the requirements of modern binder inserting units in production lines for the aforediscussed and similar stationery products.
It is also known to convert straight or coiled wire into an undulate product of the above-discussed character by resorting to machines which utilize orbiting interengaged forming tools followed by a second set of tools having wire shaping grooves and serving to impart to selected portions of undulate wire their final shape. Such wire forming machines are disclosed in U.S. Pat. Nos. 3,046,694 and 3,670,781. These machines also exhibit the drawback that the wire is subjected to very pronounced tensional stresses so that it is likely to break, especially when the speed of the machine is relatively high. Moreover, the tools of the second set are likely to come into strong frictional engagement with the material of the wire which is particularly undesirable when the wire contains a core and an outer layer surrounding the core. The outer layer is likely to be damaged, defaced or totally destroyed in response to strong frictional engagement with the tools of the second set.
It is further known to form meandering wire products in machines which utilize the aforediscussed two rows of pins, a mechanism which alternately loops the wire around successive pins of the two rows, and tongs which shape the wire in the regions of the pins so as to impart to the corresponding portions of the wire a desired shape, namely, to impart the final shape to the aforementioned webs and to the tips of the hairpin-shaped prongs. Reference may be had to U.S. Pat. Nos. 2,047,771 and 3,556,166. The output of such machines is relatively low so that their use in modern high-speed production lines for steno pads, exercise books and analogous stationery products is unwarranted.
German Offenlegungsschrift No. 2 148 915 proposes to provide the bolts of a link chain with wire forming pins and to change the mutual inclination of neighboring chain links during transport of the chain so that the distance between the neighboring pins changes. Such machine must include an additional apparatus which imparts to partially deformed wire its ultimate shape. The German publication proposes to use shaping tools in the form of worms whose deleterious effect is analogous to that of the aforementioned second set of tools in machines disclosed, for example, in U.S. Pat. No. 3,670,781, i.e., the worms are likely to damage, deface or destroy the outer layer of the wire or to exert an equally deleterious influence upon the surface of uncoated wire.